智能指针_com_ptr_t
对于COM调用,大量的AddRef/Release调用无疑是例行公事和让人生厌。
_com_ptr_t 是vc运行库中提供的固有的封装COM接口的智能指针，相比CComPtr/CComQIPtr缺少移植性，
但是支持不是ATL实现部分的的异常和操作。
以下是DirectShow中播放一个文件的代码：
IGraphBuilder *pGraph;
IMediaControl *pMediaControl;
IMediaEvent *pEvent;
// Create the filter graph manager and query for interfaces.
CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
IID_IGraphBuilder, (void **)&pGraph);
pGraph->QueryInterface(IID_IMediaControl, (void **)&pMediaControl);
pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
// Build the graph. IMPORTANT: Change string to a file on your system.
pGraph->RenderFile(L"C://Example.avi", NULL);
// Run the graph.
pMediaControl->Run();
// Wait for completion.
long evCode;
pEvent->WaitForCompletion(INFINITE, &evCode);
// Clean up.
pMediaControl->Release();
pEvent->Release();
pGraph->Release();
使用com_ptr_t后简单了很多：
//这部分可以放到头文件中
#include
_COM_SMARTPTR_TYPEDEF( IGraphBuilder , __uuidof(IGraphBuilder) );
_COM_SMARTPTR_TYPEDEF( IMediaControl , __uuidof(IMediaControl) );
_COM_SMARTPTR_TYPEDEF( IMediaEvent , __uuidof(IMediaEvent) );
...
IGraphBuilderPtr pGraph( CLSID_FilterGraph ) ;//调用CreateInstance
IMediaControlPtr pMediaControl = pGraph;//这里会自动调用QueryInterface
IMediaEventPtr pEvent = pGraph;//这里会自动调用QueryInterface
pGraph->RenderFile( L"L"C://Example.avi", NULL);
// Run the graph.
pMediaControl->Run();
// Wait for completion.
long evCode;
pEvent->WaitForCompletion(INFINITE, &evCode);
//不需要调用Release()
假如我们要复制一个接口，常常要
pG1 = pG2;
pG1->AddRef();
...
pG1->Release();
对于_com_ptr_t , 只要pG1 = pG2;就可以了
注意以下的代码：
IGraphBuilderPtr pGraph ;
pGraph.CreateInstance( CLSID_FilterGraph );
...
CoUninitialize();
因为 pGraph 会在超出作用域时析构，也就是在CoUninitialize()之后调用 IUnkown::Release() ，这样
会引起问题，可以这样解决：
pGraph.Release(); CoUninitialize();
或者
pGraph = NULL; CoUninitialize(); //这样会隐含的调用_com_ptr_t::Release()
绝对不可以调用pGraph->Release(); 因为这是调用IUnkown::Release()然后再调用一次
pGraph.Release(); 将会两次释放接口指针。
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/ljfxmf/archive/2008/06/04/2511029.aspx
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